DVL data on Bf 109 roll rates

[hitech]

These weighted some 250 pounds each, and the more weight on the wing carried, the worser the roll rate bocomes, as there`s far more intertia - see fighters like the P-38, Me 110 etc that all had engine gondolas in the wings, and even with boosted ailerons, the inertia remained a problem.

This is an incorect assumption. Stead state roll rate is not effected by inertia. And at medium and above speeds roll acceleration (i.e. the time it takes to reach max roll rate) is almost none existant.


HiTech

[gripen]

Originally posted by pasoleati
Gripen, Raunio says (in his first article in the ongoing series) that EAS is based on TAS but with compressibility correction included.

EAS as used by RAE in their documentation is not the same EAS as used in current litterature. RAE just made IAS values comparable by adding type specified corrections.

gripen

[gripen]

Originally posted by Kurfürst
OK, so you don`t have ANY details on the Spitfire roll rate test, possible modifications done, or wheter the aircraft was an avarage, above/below avarage example? So it`s a set of data which happens not to match any other data. Could it be an experimental machine?

Get the document's (DSIR 23/12865 and 23/12506 from the PRO), these give all the details you need to know.

gripen

[Kurfürst]

OK, I will check them out, but until then I think I remain sceptical.

[Angus]

Hey Gripen, have you been around the PRO?
Live in England or Frequent traveller?
I've been there, - to get deep into the stuff they have I would need a year off
And for you Kuffie, there seems to be a lot of data around about many many Spitfires to be compared with some tatty stuff about some 109's. Why do the most quoted values have to be allied values or estimations of the 109? And BTW, I did have my thoughts about the gondie effect of the 109G,- now as HiTech has replied, I expect you to challenge him on the subject or bring something unknown to the fray.
Then this:
"Angus, I don`t really get this "LOL-109mustbehigher-ergonomyposition" thing. The point was the Spitfire and 109 are again extraordinarly evenly matched in both stickforce and roll rate - neither really good at high speed btw.

I suppose even you wouldn`t call the Spitfire or the 109 an especially ergonomic plane to sit in. "

I always smell your "109mustbehigher-ergonomyposition" thing. I remember you debaiting the cockpit size of a 109 vs a P51.
Read up in Rall's book. It will do you good

[gripen]

Originally posted by  Kurfürst
OK, I will check them out, but until then I think I remain sceptical.

Well, feel free to remain skeptical but I think no one cares if you are sceptical or not. You can also easily save some work and just read the page Nashwan posted:

"This course has been adopted in Fig. 6 which shows the results obtained for the F.W.190, Mustang, Typhoon and Spitfire V (metal covered ailerons) with both standard and clipped wings. On all these aircraft instrumental recors of rolling performance have been obtained at the R.A.E. similar to those under discussion for the F.W.190."

Originally posted by Angus
Hey Gripen, have you been around the PRO?
Live in England or Frequent traveller?

I've visited PRO couple times and I'm just a frequent traveller.

gripen

[Knegel]

Originally posted by Kurfürst
Kneagel I think you took the IAS/TAS conversion wrong.

Here`s my version. I used a Rechlin flight test that lists both IAS and TAS for 3000m, so it`s more accurate to show German conditions. IAS conversion is effected by a lot of factors, and standard day conditions are different from country to country, so even small errors can lead to big differences, see below.

I used  1 IAS = 0.861 TAS conversion, not the scientific gripen "roughly 20%". It should reflect German IAS conversion standards.


ERRATA : The blue "30 lbs" (I don`t know if it`s conversion quality error or typo) is showing the 50 lbs line for the Bf 109, not 30 lbs !

I don`t really see how the roll rate bad. It`s about avarage on the whole range in the group.

Hi,

i dont think i got the calculation wrong!

Lets take the 30lb(13,6) peak value.

We miss this exact line, but i estimate it at almost exact 1.2 rad, 400km/h TAS.

400km/h = 248,6mph TAS, your 30lb IAS peak show a much greater IAS than TAS, so you probably was in a  3000m deap valley!

If i take your factor of 1 IAS = 0.861 TAS.

248,6mph  x 0,861 = 214mph, my graph show 208mph, i think thats a pretty smal error.  The Airspeedcalculator use factor 0,8492 for 3000m alt.

Sometimes the will to find a wanted result lead us to make bad mistakes! I realy would have liked to find a better 109 rollratio, and my initial wrong interpretation made me believe that, but the result simply show what is long time well known!

btw: "I used a Rechlin flight test that lists both IAS and TAS for 3000m." Could you please show this test, if you realy took your 30lb line from a Rechlin test, i wonder why your 66lb line fit to mine?
never theless, this 109F test is only one, and as you see, we have already 3 different Spitfire metal aleron curves, plus the Mustang/Spitcomparison, and all show different results.
Would be interesting, if they made tests with other aleron adjusting.

Yep gripen, i simply agreed to you, regarding the rollratio.

Yes, some NACA tests show comparisons up to 400mph and more, NACA tests of the HurricaneII (L-565) and the SpitfireVa(L-334), next to the Spit/Hurri/P36/P40 comparison, stop at 300 eg. 320mph. Looks like they dont thought that tests above this speed are of any use.  I only wanna show that the rollratio at highest speeds shouldnt get overvalued!

Greetings, Knegel

Edit: Just understood your "errata" message! Your 30lb/50lb line is the 30lb line in a 3000m deap valley, you took 248 / 0,861 = 285mph, instead of 248 x 0,861 = 214mph.

[niklas]

Originally posted by gripen


Tested planes were standard Spitfire Vs. The most probable reason for the difference between NACA and RAE data is that there appear to be plenty of loosenes in the aileron linkage of the NACA tested Spitfire and Hurricane; the roll rate curves does not show typical sharp edges when the stick force limit is reached. The RAAF data on Spitfire V shows quite good agreement with RAE data given the different stick force and the both data sets show typical sharp edges.

gripen

Any flying times of the 109F2 known? Was it factory fresh, or also used for other tests earlier?
We should never forget that this report was NOT made to determine the highest rolling velocity of the 109 series, especially not of factory fresh aircrafts, but to confirm theoretical models!
Furthermore we should never forget that tests were down in 3 different countries, everywhere maybe with different instrumentation, TAS/ IAS is different, power setting was different, and so on. 109F was always flying with full tanks too.

When SpitVA was flown quite often than it´s great data, isn´t it? I mean  it represents aircrafts in service condition, probably after higher G-loads. And why should loseness affect stick force?

The spit was a light plane for it´s size, one would assume a rather flexible wing. Ok, the "sharp edge" in the naca chart is at low speeds, nevertheless i´d assume even there the influence of wing twist like in other curves that is not shown. I have my doubts about it, seriously, and i consider the naca chart way more realistic.
Oh btw - it is well known that the 190 curve is the worst they measured out of three. So if you intentionally take the worst of the enemy, you take what ? The best of your own of course!

niklas

[Angus]

Hehe, - this:
"The spit was a light plane for it´s size, one would assume a rather flexible wing"
FYI, the wing was flexible, as were other WW2 fighter wings. However the Spitfire wing was VERY strong and much stronger than many other. So, while I know it was made stiffer in later models, I rather doubt it flexed any more than most.

[niklas]

Originally posted by Angus

FYI, the wing was flexible, as were other WW2 fighter wings. However the Spitfire wing was VERY strong and much stronger than many other

Probably one more of your theories that you can only backup by some stories (in best case) i suppose. Actually you probably don´t even know about what stiffness we are speaking.

niklas

[Nashwan]

Oh btw - it is well known that the 190 curve is the worst they measured out of three. So if you intentionally take the worst of the enemy, you take what ? The best of your own of course!

No, I think it's the only one they measured. What they said was:

It should be pointed out, however, that where Frise ailerons are used, there is liable to be a variation in the feel of the control from aircraft to aircraft.  Our pilots, who have now flown three Fw 190s, have, in fact, noticed this variation; they report that the machine on which the measurements were made had rather heavier ailerons than the other two.

I don't know how comfortable you are with English, but the tense of the last sentence implies the tests were made before the other aircraft were flown, and that the other aircraft have been flown but not fully tested.

[niklas]

You´re right in this case. But why did they take the heaviest one for testing when they knew about 2 better ones?

niklas

[Nashwan]

I don't think they knew about the 2 lighter ones until after the tests.

The test was of Pe882, I believe. That was captured after it landed in Britain in error on 17th April 1943 (according to Brown). The report is dated July 1943, and obviously the tests took place before that.

The 2 others refered to in the report are probably those that landed in Britain on the 20th May and 20 June 1943.

I should think the tests were run some time in April or May, either before the 2nd plane was captured, or before they became aware there were aileron differences between the aircraft.

[gripen]

Originally posted by niklas
Any flying times of the 109F2 known? Was it factory fresh, or also used for other tests earlier?

As you allready know, the report does not give much details about the test plane. It's just described as a "sample" and it was a  prepared test bed with special instrumentation. Probably it was one of those planes which these organizations used for various tests. Anyway, nothing indicates that it was in bad condition.
 
From earlier discussion you probably remember that the only oddity I can see is mean average deflection which is not same as given in the specs (when measured without load). That might be measurement error or just normal production variation.

Originally posted by niklas

We should never forget that this report was NOT made to determine the highest rolling velocity of the 109 series, especially not of factory fresh aircrafts, but to confirm theoretical models!

Yep, it can be seen that the tested sample did very close to theoretical models ie it's condition was very close to what it was supposed to be.
 

Originally posted by niklas
When SpitVA was flown quite often than it´s great data, isn´t it? I mean  it represents aircrafts in service condition, probably after higher G-loads. And why should loseness affect stick force?

The loosenes "might" affect on stick forces by increasing the stick movement for given aileron deflection ie in a way there is more leverage at the speeds where the full stick deflection can't be reached. But that depends on geometry of the linkage.

Originally posted by niklas
The spit was a light plane for it´s size, one would assume a rather flexible wing. Ok, the "sharp edge" in the naca chart is at low speeds, nevertheless i´d assume even there the influence of wing twist like in other curves that is not shown. I have my doubts about it, seriously, and i consider the naca chart way more realistic.

It can be easily seen that in the case of the NACA tested Spitfire V, the aileron linkage (probably too low tension in the controll cables) start to show large amount of elasticity at low speeds before the stick force limit is reached and removing the typical sharp edge when the stick force limit is reached (the roll rate still increase after a small edge). That indicates poor mainteance because other tests by RAE and RAAF show logical sharp edge (ie the roll rate decrease after the sharp edge). Service planes probably showed same kind of symptons but that is arguable and depends on mainteance.

Notable thing regarding the wing twist is that RAE comments on the NACA report on Spitfire claim:

"Stability and control in a high speed dive. This was not touched, since the highest speed attained during the tests was 295 m.p.h. Vi. Neglect of the vital speed region round 400 m.p.h. Vi resulted in erroneous conclusions being drawn from the measurements at lower speeds. For example it is stated that "there was very little reduction in aileron effectiveness either by separation of flow near minimum speed or by wing twist at high speed." Actually, of course, loss of aileron power due to wing twist at high speeds is one of our biggest problems on the Spitfire - at 400 m.p.h. Vi about 65% of the aileron power is lost thereby."

Originally posted by niklas
Oh btw - it is well known that the 190 curve is the worst they measured out of three. So if you intentionally take the worst of the enemy, you take what ? The best of your own of course!

AFAIK they made instrumented tests just with one plane and that just happened to have heaviest ailerons of the three.

Originally posted by Nashwan

The test was of Pe882, I believe. That was captured after it landed in Britain in error on 17th April 1943 (according to Brown). The report is dated July 1943, and obviously the tests took place before that.

Yep quite probably the PE882, the report on it claims that:

"Perhaps owing to rigging, the lateral control, though still good, was not nearly so light at high speeds as in former aircraft."

The "former aircraft" means the MP499.

gripen

[Kurfürst]

Originally posted by niklas
Any flying times of the 109F2 known? Was it factory fresh, or also used for other tests earlier?

[/B]

Well considering the tests was done in June 1944, and the 109F-2 was only produced between November 1940 - August 1941, the machine itself was 3-3.5 years old.

Originally posted by niklas
Furthermore we should never forget that tests were down in 3 different countries, everywhere maybe with different instrumentation, TAS/ IAS is different, power setting was different, and so on. 109F was always flying with full tanks too.?

[/B]

Yep. Even though if the instrumentation would be just as good everywhere, the power would strongly effect the rate of roll (the 109F-2 was only flown at continous power), and the RAE typically did it`s trials without guns and ammo, half fuel load.
The most serious issue in comparing with the NACA chart is IAS/TAS conversion, it would displace the original graph left or right on the speedscale, and even small conversion differencies can have big effect.

The spit was a light plane for it´s size, one would assume a rather flexible wing. Ok, the "sharp edge" in the naca chart is at low speeds, nevertheless i´d assume even there the influence of wing twist like in other curves that is not shown. I have my doubts about it, seriously, and i consider the naca chart way more realistic.
niklas [/B]

Yep, that`s my line of thinking as well. NACA 868 notes some 65% reduction of roll rate for the Spitfire due to wing twist, but curiously, there is no sign of that on the RAE curves they copied. I guess there`s more in the original report on that, it`s just a bit 'filtered'.